Oil and water don’t mix, and neither do gasoline and diesel fuels. Not until now, anyway. But that old rule could soon go out the door.
Chrysler and the U.S. Department of Energy are developing a radical engine design that burns a combination of gasoline and diesel fuels. If the prototype works, it could help Chrysler and other automakers meet tough new fuel economy targets that will be phased in over the next 15 years, according to a presentation given by Chrysler during the DOE’s 2011 Merit Review in Washington D.C.
The small-displacement, 2.4-liter turbocharged four-cylinder multi-fuel engine promises up to a 25% improvement in city and highway fuel economy for a Chrysler minivan, compared to a 2009 4.0-liter V-6, while maintaining similar performance. That would mean that the new engine could yield as much as 31 mpg on the highway in a Town & Country.
The 4.0-liter V-6 in the 2009 Chrysler minivan was rated 17 mpg City, and 25 mpg Highway, while pumping out 251 horsepower and 259 pounds-feet of torque.
Until now, gasoline and diesel have been considered mutually exclusive automotive fuels because of their unique chemical and combustion properties. Gasoline engines use a so-called Otto combustion cycle, in which a combination of gas and air are mixed and compressed in an engine’s cylinders and ignited using a spark plug to produce power.
Diesel engines follow the so-called diesel combustion cycle, where air is compressed to such a high degree that friction causes injected diesel fuel to ignite without a spark. Higher compression and greater energy density per gallon is what gives diesel about a 20% to 30% fuel economy advantage over gasoline.
Chrysler’s bi-fuel engine design calls for a three-valve head with two direct-injection gasoline fuel injectors and a single diesel injector. Two turbos – one high-pressure and one low-pressure – will provide two-stage turbocharging to meet boost requirements supporting a high compression ratio for power and fuel economy.
Exhaust gas cooling and metered injection of diesel fuel will be used to control knock, or the premature detonation of a gasoline fuel-air mixture that can damage an engine under high compression loads.
“The addition (and timing) of diesel fuel has a significant impact on burn rate,” the presentation noted.
In this respect, Chrysler’s gasoline-diesel engine appears to follow a similar approach to Ford’s prototype bi-fuel engine, which used a mixture of gasoline and ethanol. The practical limitation of Ford’s engine would be the limited availability of ethanol in the real world, whereas diesel has widespread distribution across the U.S.
Both engines are also practically limited by the need for separate fuel tanks so the fuels aren’t mixed before combustion. In the real world, it’s not hard to imagine the extra hassle posed by filling up a vehicle at both the gas and diesel pumps.
Chrysler’s demonstration vehicle will show several other fuel-saving features, including shutting off fuel to the engine during vehicle braking, mild hybrid start-stop engine shutoff at stoplights and using waste engine heat to generate electricity to power some vehicle accessories instead of drawing accessory power from the engine.
The multifuel project is being funded with $30 million; Chrysler and its partners – including Delphi, FEV, Ohio State University and Argonne National Laboratory – are putting up $15.5 million, and the Department of Energy is putting up $14.5 million. It runs through April 2013.
The DOE published the full set of presentations from the 2011 Merit Review last week. We’ve asked Chrysler for comment about the project by e-mail but haven’t heard back yet.
The U.S. maker has frequently pushed development of quirky, if creative, powertrain alternatives. A decade ago, a time when there was significant interest in fuel cell technology, Chrysler proposed an approach that would use a slurry of sodium borohydride, rather than liquid or compressed hydrogen gas.
Mike Levine is editor and publisher of PickupTrucks.com.